1. Field of the Invention
The invention relates to a capacitive pulse pickup having a capacitor electrode which is adapted to be placed against an ignition cable or the like.
2. Description of the Prior Art
Pulse pickups of the above type are known from U.S. Pat. No. 3,474,667. These pickups are inexpensive to manufacture, are rugged and easy to handle. However, they have one disadvantage which often leads to measurement errors. In particular, it is found that the capacitive pickups respond not only to voltage changes in their immediate vicinity, but also to voltage changes in their farther removed surrounding environment. As a result, faulty pulses are generated which lead to erroneous results.
In U.S. Pat. No. 3,543,572, for example, there are also described inductive type pulse probes or pickups which are less sensitive to undesired stray influences. When an inductive probe is used for picking up the ignition pulses of an ignition system of an externally fired internal-combustion engine, operation of the probe depends upon the charging current of the charging circuit of the ignition system, as the firing current proper of the ignition spark has no pulse-like rise. The charging current, however, depends on the total capacity of the ignition system which has a different magnitude for each type of motor vehicle. It is, therefore, difficult to design a single inductive probe for all ignition systems.
It is an object of the present invention to provide an improved capacitive pulse pickup.